The invention relates to a process for casting a mounting which is to be attached to a human body and which takes the form of a prosthesis socket or of an orthosis part with internal reinforcement in the shape of a grid or frame.
A prosthesis is an artificial replacement for an amputated limb that is secured to the remainder of the limb and specifically and particularly to the amputated limb. To this end, the prosthesis has a receptacle in the shape of a funnel or cup for the amputated limb, hereinafter termed “prosthesis socket”. Ideally, the prosthetic socket is intended to precisely fit the amputated limb and to an produce a transfer of force from the amputee's body to the prosthesis with no significant areas generating pressure or chafing. If possible, the socket should be capable of elastic adaptation to small dimensional changes of the limb (for example, when the amputated limb swells and reverts to normal size after swelling).
There are similar requirements placed upon what are known as orthoses or those retaining parts which are close to the body. Orthoses are devices which externally hold and support the body or limbs of the body, often being termed braces or splints.
In order to meet the requirements, sockets and other orthopaedic holders (orthoses) that directly contact the body are generally manufactured from plastics which while strong and dimensionally stable, have at least some regions of elasticity or softness and pliability.
To this end, it is common to combine various plastics in a plurality of layers, and within plastic layers, to provide reinforcement, composed of, e.g., woven or knitted materials or of carbon fibers (generally in the form of carbon-fiber mats). It is also possible that the reinforcement is used specifically in certain zones of the mounting component, or that certain, e.g. particularly soft, materials in the manner of an adhesive plaster (cushioning, patches) are substituted for the main material in selected regions or are included in addition to the main material.
Techniques used to construct laminates with polymer-saturated textile reinforcement include winding or casting. These are industrial processes known to orthopaedic technologists. The winding technique winds bandages saturated with an incompletely reacted polymer onto a form, or if appropriate, directly onto the limb stump. The wound capsule is then permitted to harden. As an alternative, saturated textile stockings can be applied in one or more layers to a form. This technique is also often used for structures composed of plaster of Paris, including models made from plaster of Paris (positive cast replica, negative cast replica).
The casting technique casts an incompletely hardened or reacted liquid polymer into a suitable socket cavity or mounting cavity which can be formed from the male mold of the limb stump and a female mold obtained with the aid of a spacer medium over the male mold. The spacer medium is either removed prior to casting (e.g., unfilled mold casting) or, in the case of a porous spacer medium, can be incorporated concomitantly, i.e. incorporated in the casting, so that a filled or reinforced component is produced. In particular, the spacer medium can be a porous filler (e.g., hardened foam or solid granules) or can be composed of textile layers or other layers that absorb liquid (e.g., wound bandages, stocking, socks and textile sublayers in general). A suction technique is often used to facilitate casting into narrow hollow molds. While the liquid and generally viscous polymer precursor (e.g., prepolymers or mixture of starting materials) is cast or injected into the hollow mold, air is sucked out from the same space (generally at another point by way of a valve) in order to facilitate the inflow of the liquid.
Very high-viscosity materials which cannot be cast are often spread onto a male mold, textile sublayers or reinforcement sublayers situated thereover.
EP 201 884 A1 discloses a process for producing a prosthesis with a socket in which a conventional winding-casting technique is used that includes cushioning composed of a viscoelastic material. The socket is composed of the saturated winding bandages and is relatively stiff. While the cushioning can mitigate pressure points, it does not have the necessary elasticity for ideal transmission of pressure- and shear-derived forces.
EP 650 708 B1 discloses a multiple-stage process for producing a socket and a lining. The process is intended inter alia to ensure full contact between the socket and the amputated stump and to increase the transmission of impact- and shear-derived forces. The soft elastic lining is composed of a viscoelastic polyurethane which is produced from an aromatic diisocyanate and elasticizing polyols. The two-part structure composed of the socket and the lining individually and extensibly molded on the amputated stump is troublesome for the user to apply and is often perceived as constricting. The lining does not remove the additional need for the socket to be designed in a relatively complex manner with regions of varying stiffness, elasticity and softness to increase comfort.
There are also known sockets composed of polyurethane which are dimensionally stable but which have the softness and elasticity to reversibly deform under pressure, with interior reinforcement in the form of a relatively stiff frame or grid. By way of example, a carbon-fiber-reinforced windowed polyacrylate layer forms the frame. A disadvantage found with these sockets manufactured from a plurality of individual layers is that the layers can separate from one another, in particular at the edges, making the sockets unusable over time.